Process for neutralization of petroleum acids using overbased detergents

ABSTRACT

The invention relates to a process for treating naphthenic acid containing whole crudes or fraction thereof to reduce or eliminate their acidity by contacting the acidic whole crude or fractions thereof at a suitable temperature typically of less than 200° C. with a neutralizing amount typically from 0.25:1 up to 10:1 of overbased detergent. The process has the additional benefits of reducing materials handling problems associated with emulsion formation in treated crudes.

This is a continuation-in-part of U.S. Ser. No. 519,279 filed Aug. 25,1995, abandoned and also a 371 of PCT/US96/13689 filed Aug. 23, 1996.

FIELD OF THE INVENTION

The present invention relates to a process for neutralizing petroleumacids in order to lower their corrosivity and increase their value.

BACKGROUND OF THE INVENTION

Whole crudes with high petroleum acid content such as those containingnaphthenic acids are corrosive to the equipment used to extract,transport and process the crudes.

Efforts to minimize naphthenic acid corrosion have included a number ofapproaches. U.S. Pat. No. 5,182,013 refers to such recognized approachesas blending of higher naphthenic acid content oils with low naphthenicacid content oils. Additionally, a variety of attempts have been made toaddress the problem by using corrosion inhibitors for the metal surfacesof equipment exposed to the acids, or by neutralizing and removing theacids from the oil. Examples of these technologies include treatment ofmetal surfaces with corrosion inhibitors such as polysulfides (U.S. Pat.No. 5,182,013) or oil soluble reaction products of an alkynediol and apolyalkene polyamine (U.S. Pat. No. 4,647,366), or by treatment of aliquid hydrocarbon with a dilute aqueous alkaline solution, specificallydilute aqueous NaOH or KOH (U.S. Pat. No. 4,199,440). U.S. Pat. No.4,199,440 notes, however, that a problem arises with the use of aqueoussolutions that contain higher concentrations of base. These solutionsform emulsions with the oil, necessitating use of only dilute aqueousbase solutions. U.S. Pat. No. 4,300,995 discloses the treatment ofcarbonous materials particularly coal and its products such as coalliquids, vacuum gas oils, and petroleum residua having acidicfunctionalities, with a dilute quaternary base such astetramethylammonium hydroxide in a liquid (alcohol or water).

While these processes have achieved varying degrees of success there isa continuing need to develop more efficient methods for treating theseacidic crudes, whole crudes and fractions thereof.

SUMMARY OF THE INVENTION

The present invention provides for a process for decreasing the acidityof an acidic crude oil comprising: contacting a naphthenicacid-containing crude oil at an elevated temperature with an effectiveamount of overbased detergent dispersed in oil to produce a treatedcrude oil having a reduced acidity. Preferably the overbased detergentis a calcium sulfonate or phenate. The amount of overbased detergentshould be effective to decrease the acidity of the crude and preferablycan range from 0.025:1 to 10:1 moles of calcium to acidic functionalityin the crude oil.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed.

DETAILED DESCRIPTION OF THE INVENTION

Some whole crude oils and fractions thereof contain organic acids thatcontribute to corrosion or fouling of refinery equipment. These organicacids generally fall within the category of naphthenic and other organicacids. Naphthenic acids alone or in combination with other organic acidssuch as phenols can cause corrosion at temperature ranges of about 65°C. (150° F.) to 420° C. (790° F.).

The crudes that may be used are naphthenic acid-containing crude oils oracid-containing fractions thereof including whole and topped crudes,that are liquid or liquefiable at the temperatures at which the presentinvention is carried out. Whole crudes are unrefined, undistilledcrudes.

Applicants have discovered that acidic crudes, i.e., those containingnaphthenic acids may be treated by contacting the crude with aneffective amount of an oil (hydrocarbon) dispersible basic reagent toproduce a treated or final crude having a reduced or essential absenceof acidity. This is accomplished by neutralizing in whole or in part theacidity of the crude. The naphthenic acids may be present either aloneor in combination with other organic acids, such as phenols. Theoil-dispersible basic reagents are called overbased detergents and arefurther described below. The acidic crudes are preferably whole crudes.However, acidic fractions of whole crudes, such as topped crudes, 500⁺ °F. (260⁺ ° C.), 650⁺ ° F. (343⁺ ° C.) fractions, vacuum gas oils and1050⁺ ° F. (565⁺ ° C.) fractions also may be treated.

An additional benefit is the absence or substantial absence of emulsionformation. Emulsion formation is an undesirable and a particular problemthat is encountered during treatment of naphthenic acid-containingcrudes with aqueous bases. The formation of a crude oil-aqueous emulsiontends to interfere with the efficient separation of the crude oil andwater phases and thus with recovery of the crude oil. Thus, in additionto their corrosivity, naphthenic acids must be removed from the crudeoil due to their tendency to encourage emulsion formation duringprocessing.

The term stoichiometric amount means a sufficient amount of overbaseddetergent on a moles basis to neutralize a mole of acidic functionalityin the crude oil. For example, in the case of calcium overbaseddetergent the ratio is 0.5:1 moles of calcium to acid content in thestarting crude. The terms "above", "greater than" or "in excess ofstoichiometric, and the term "substoichiometric" and "less thanstoichiometric" are defined in relation to the foregoing and will varyaccording to the valence of the metal cation.

The contacting is typically carried out at an elevated temperaturesufficient to reflux the solution. Typically, this is less than 200° C.,preferably from 20° C. to 200° C., however, temperatures of from about100° C. to 170° C. also may be used. Desirably this results inneutralization of the naphthenic acids in the crude oil.

The oil dispersible basic reagents (overbased detergents) may bepurchased commercially or synthesized using known procedures. Preferredin this invention are the overbased sulfonate and phenate detergentsprepared from calcium, and those containing at least 3 wt % calcium aremost preferred.

The overbased detergent is added to the acidic crude in an amounteffective to produce a neutralized (fully or partially, as desired)final crude oil, i.e., a crude having a decreased acidity from thestarting crude. Broadly, ratios ranging in effective amounts of from0.025 moles to 10:1 moles, or 0.25 to 10:1, or 0.025 to 5:1, and 0.5:1to 5:1 may be used. Thus, stoichiometric amounts of calcium to acidicfunctionality in the crude to higher mole ratios of overbased detergentto total acid of from 1:1 to about 10:1, preferably of from 2:1 to 1:1,to lower ratios, e.g., substoichiometric amounts, such as 0.025:1 molesup to a stoichiometric amount, preferably 0.25:1 moles up to astoichiometric amount, as effective, may be used to achieve suitablelevels of acid decrease. The addition of smaller (than stoichiometric)amounts of overbased detergent may result in an incomplete (i.e.,partial neutralization) neutralization of the starting crude.

Reaction times depend on the temperature and the nature of the crude tobe treated, its acid content, and the amount and type of overbasedcalcium phenate or sulfonate detergent added, but typically may becarried out for from less than about 1 hour to about 20 hours to producea product having a decrease in naphthenic acid and other acid content.

The concentration of acid in the crude oil is typically expressed as anacid neutralization number or acid number, which is the number ofmilligrams of KOH required to neutralize the acidity of one gram of oil.It may be determined according to ASTM D-664. Typically, the decrease inacid content may be determined by a decrease in the neutralizationnumber or intensity of the carboxyl band in the infrared spectrum atabout 1708 cm⁻¹. Crude oils with total acid numbers (TAN) of about 1.0and lower are considered to be of moderate to low corrosivity (crudeswith a total acid number of 0.2 or less generally are considered to beof low corrosivity). Crudes with total acid numbers greater than 1.5 areconsidered corrosive. Acidic crudes having free carboxyl groups may beeffectively treated using the process of the present invention. The IRanalysis is particularly useful in cases in which a decrease inneutralization number is not evident upon treatment with the base asufficient measure of acidity, as has been found to occur upon treatmentwith bases weaker than KOH.

While not wishing to be bound by any theory it is believed that thereaction takes place by neutralization of the acid groups on thenaphthenic acid in the presence of inverse micelles of calcium carbonatedispersed in oil.

Whole crude oils are very complex mixtures in which a large number ofcompeting reactions may occur. Unexpectedly, the reaction occursalthough the acid is dilute in comparison to the large excess of crudeand other reactive species typically present.

The process of the present invention has utility in processes in whichinhibiting or controlling liquid phase corrosion, e.g., of metalsurfaces, is important. More generally, the present invention may beused in applications in which a reduction in the acidity, typically, asevidenced by a decrease in the neutralization number of the acidic crudeor a decrease in intensity of the carboxyl band in the infrared spectrumat about 1708 cm⁻¹ of the treated (neutralized) crude, would bebeneficial and in which oil-aqueous emulsion formation is not desirable.The present invention also provides a method for controlling emulsionformation in acidic crudes, by treating a major contributing componentof such emulsions, naphthenic and similar organic acids.

The present invention may be demonstrated with reference to thefollowing non-limiting examples.

EXAMPLE 1

The reaction apparatus was a flask equipped with stirrer, and refluxcondenser, immersed in an oil bath. 50 g of San Joaquin Valley crude,having a neutralzation number of 4.17 mg KOH/g was put into the flask.Then 1.8 g of an overbased calcium detergent dispersion in oil, having abase content equivalent to 135 mg KOH/g were added. The mixture wasstirred at 100° C. for 8 hours, then cooled. The treated liquid had aneutralization number of 3.51 mg KOH/g. That corresponded to 83% of theoriginal acidity still present. However, examination by infraredspectroscopy showed that the band at 1708 cm⁻¹, corresponding to thecarboxyl group, had an intensity corresponding to only 26% of that ofthe untreated crude.

EXAMPLE 2

The reaction apparatus was the same as in Example 1. 50 g of the samecrude used in Example 1 was put into the flask. 0.96 g of an overbasedcalcium sulfonate detergent dispersion in oil, having a base contentequivalent to 252 mg KOH/g, was added. The mixture was stirred at 100°C. for 8 hours. The neutralization number had dropped to 2.84 mg KOH/g.

EXAMPLE 3

The reaction apparatus was the same as in Example 1. 50 g of the samecrude used in Example 1 was put into the flask. 0.61 g of an overbasedcalcium sulfonate detergent dispersed in oil and having a base numberequivalent to 400 mg KOH/g was added. The mixture was heated at 100° C.for 8 hours. The liquid had a neutralization number of 3.20 mg KOH/g.That corresponded to 76% of the original acidity. However, examinationby infrared spectroscopy showed that the band at 1708 cm⁻¹,corresponding to the carboxyl group, had an intensity corresponding toonly 26% of that of the untreated crude.

EXAMPLE 4

The reaction apparatus was the same as in Example 1. 50 g of the samecrude used in Example 1 was put into the flask, followed by 2.5 g of theoverbased detergent used in Example 2. The mixture was stirred at 100°C. for 8 hours. The liquid had a neutralization number of 2.79 mg KOH/g.That corresponded to 67% of the original acidity. However, examinationby infrared spectroscopy showed that the band at 1708 cm⁻¹,corresponding to the carboxyl group, had an intensity corresponding toonly 9% of that of the untreated crude.

EXAMPLE 5

The reaction apparatus was the same as in Example 1. 50 g of the samecrude used in Example 1 were put into the flask, followed by 9.6 g ofthe overbased reagent used in Example 2. The mixture was stirred at 100°C. for 6 hours. The liquid had a neutralization number of 2.45 mg KOH/g. That corresponded to 58% of the original acidity. However, examinationby infrared spectroscopy showed that the band at 1708 cm⁻¹,corresponding to the carboxyl group, had virtually disappeared.

We claim:
 1. A method for decreasing the acidity of an acid-containingcrude oil comprising: contacting a starting naphthenic acid-containingcorrosive crude oil at an elevated temperature with an effective,naphthenic acid decreasing amount of overbased detergent wherein theoverbased detergent is selected from the group consisting of calciumsulfonates and phenates to produce a treated crude oil having a reducednaphthenic acid content.
 2. The method of claim 1 wherein the oil is anacidic whole crude oil.
 3. The method of claim 1 wherein the oil is anacidic crude fraction.
 4. The method of claim 1 wherein the amount ofoverbased detergent is from 1:1 to 10:1 calcium to acidic functionalityin the starting crude oil.
 5. The method of claim 1 wherein the amountof overbased detergent is from 0.025:1 to 10:1 moles of calcium toacidic functionality in the starting crude oil.
 6. The method of claim 1wherein the amount of overbased detergent is 0.25:1 to 10:1 moles ofcalcium to acidic f unctionality in the starting crude oil.
 7. Themethod of claim 1 wherein the amount of overbased detergent is less thana stoichiometric amount of calcium to acidic fuznctionality in thestarting crude oil.
 8. The method of claim 1 wherein the amount ofoverbased detergent is from 0.025:1 to 5:1 moles of calcium toacidicfunctionality in the starting crude oil.
 9. The method of claim 1wherein the overbased detergent is added in a ratio from about 0.5:1 to5:1 moles of calcium to acid content of the starting crude oil.
 10. Themethod according to claim 1, wherein the overbased detergent ispartially carbonated.
 11. The method of claim 1 wherein the startingcrude oil has a neutralization number of from about 0.5 to 10 mg KOH/g.12. The method of claim 1 wherein the starting crude oil has aneutralization number of from about 0.2 to 10 mg KOH/g.
 13. The methodof claim 1 wherein the temperature is from about 20° C. to 200° C. 14.The method of claim 1 wherein the temperature is from about 100° C. to170° C.
 15. The method of claim 1 wherein the contacting produces atreated crude oil containing a carboxylate salts of naphthenic acids.16. The method of claim 1 wherein the reduction in acidity of thetreated crude oil is produced in the substantial absence of emulsionformation.